Answer:
What has a bell but isn't a church. Is full of air but is not a balloon?
Looks like water, but it's heat. Sits on sand, lays on concrete. A play on the eyes, but it's all lies.
It holds most knowledge that has ever been said. But is not the brain, is not the head. To feathers and their masters, it's both bane and boonΒ One empty, and one full.
Tool of thief, toy of queen. Always used to be unseen. Sign of joy, sign of sorrow. Giving all likeness borrowed.
By Moon or by Sun, I shall be found. Yet I am undone, if there's no light around.
Dark, feathery, and popular in Baltimore and fantasy books.